JP2006260909A - Membrane electrode assembly and polymer electrolyte fuel cell using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an MEA which has an excellent power generation property containing a non-platinum catalyst at a low production cost as well as a PEFC using the above MEA. <P>SOLUTION: The membrane electrode assembly (MEA) 20 is composed of an anode catalyst layer 110 containing a palladium alloy, a conductive carbon material carrying the above palladium alloy, and a proton conductive polyelectrolyte, a solid polyelectrolyte membrane 100, a cathode catalyst layer 110 containing a catalyst, a conductive carbon material carrying the above catalyst, and the proton conductive polyelectrolyte. The MEA 20 is used as a structural part of a polymer electrolyte fuel cell (PEFC) 10. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a membrane electrode assembly (hereinafter also referred to as “MEA”) and a polymer electrolyte fuel cell using the same. More specifically, the present invention relates to an improvement in the MEA catalyst layer.

  In recent years, fuel cells have attracted attention as vehicle drive sources and stationary power sources in response to social demands and trends against the background of energy and environmental problems. Fuel cells are classified into various types depending on the type of electrolyte, the type of electrode, and the like, and representative types include alkaline type, phosphoric acid type, molten carbonate type, solid electrolyte type, and solid polymer type. Among them, a polymer electrolyte fuel cell (PEFC) that can operate at a low temperature (usually 100 ° C. or less) attracts attention, and in recent years, development and practical application as a low-pollution power source for automobiles is progressing. As a PEFC application, a vehicle drive source and a stationary power source have been studied, but in order to be applied to these applications, durability over a long period of time is required.

  In general, the PEFC has a structure in which an MEA is sandwiched between separators. In MEA, a gas diffusion layer, an anode (fuel electrode) catalyst layer, a solid polymer electrolyte membrane, and a cathode (air electrode) catalyst layer are generally laminated in this order, and the laminate is formed by a pair of gas diffusion layers. It has a sandwiched structure. The battery reaction proceeds in a catalyst layer comprising a catalyst, a carrier supporting the catalyst, and an ion conductive polymer.

  When a PEFC is used for a long-term use such as a vehicle, the PEFC is required to have excellent durability. Various causes can be considered as a cause of lowering the power generation characteristics of PEFC. One of the causes is elution of the catalyst metal to the solid polymer electrolyte membrane, which is likely to occur on the cathode side. The catalyst metal is ionized by the start / stop of the PEFC or the potential fluctuation, and flows out to the solid polymer electrolyte membrane. The metal ions flowing out to the solid polymer electrolyte membrane associate with hydrogen gas, and the metal is deposited in the solid polymer electrolyte membrane. Due to the reduction of the catalyst by such a mechanism, the power generation characteristics of the PEFC are deteriorated.

Accordingly, platinum and platinum alloys that have high catalytic activity and are difficult to ionize are used as the catalyst disposed in the PEFC catalyst layer (see, for example, Patent Document 1). However, since platinum is a resource unstable and expensive material, it is desired to develop a catalyst made of a cheap and resource stable material.
JP 2005-32668 A

  An object of the present invention is to provide an MEA containing a non-platinum-based catalyst as a catalyst at a low production cost and excellent in power generation characteristics. Another object of the present invention is to provide a PEFC having the MEA.

  The present invention relates to an anode catalyst layer including a palladium alloy, a conductive carbon material supporting the palladium alloy, and a proton conductive polymer electrolyte, a solid polymer electrolyte membrane, a catalyst, and a conductive carbon supporting the catalyst. A membrane electrode assembly having a material and a cathode catalyst layer containing a proton conductive polymer electrolyte. The present invention also provides a polymer electrolyte fuel cell having the membrane electrode assembly.

  By using a palladium alloy as a catalyst in the anode catalyst layer of MEA, it is possible to produce MEA having excellent power generation characteristics at a low cost. As a result, it is possible to manufacture a PEFC having excellent power generation characteristics at a low cost.

  Compared to platinum-based catalysts, palladium-based catalysts are inexpensive but have poor power generation performance and tend to be inferior in stability under strong acidity. In general, the acid resistance is Pt≈Pt-Co> Pd-Co> Pd. Here, considering the stability under strong acidity, the phenomenon that platinum is ionized and eluted into the solid polymer electrolyte membrane is likely to occur on the cathode side, and the use environment is relatively gentle on the anode side. In light of this fact, research progressed, and in the anode catalyst layer, it was possible to produce PEFCs with excellent characteristics even when palladium-based catalysts were used instead of platinum-based catalysts, reducing the manufacturing costs of MEA and PEFC. I knew it was possible. That is, in the present invention, a palladium alloy is used as a catalyst for the anode catalyst layer.

FIG. 1 is a schematic cross-sectional view of a PEFC in which an MEA in which a gas diffusion layer, an anode catalyst layer, a solid polymer electrolyte membrane, a cathode catalyst layer, and a gas diffusion layer are stacked in this order is sandwiched by a pair of separators. . As shown in the figure, the PEFC 10 has a cathode supplied with an oxidant and an anode supplied with hydrogen gas disposed on both sides of the solid polymer electrolyte membrane 100. The cathode and anode have a catalyst layer 110 and a gas diffusion layer 120, respectively. MEA 20 is configured by solid polymer electrolyte membrane 100, catalyst layer 110, and gas diffusion layer 120. A separator 130 and a current collector 140 are disposed outside the MEA 20. A flow path 135 is formed in the separator 130. An oxidant such as air is supplied to the cathode-side channel 135, and hydrogen gas is supplied to the anode-side channel 135.
The PEFC configuration is not limited to the embodiment shown in FIG. For example, a water repellent layer for preventing a flooding phenomenon is disposed between the catalyst layer 110 and the gas diffusion layer 120.

Hereinafter, each component of MEA and PEFC will be described in detail in order.
The anode catalyst layer 110 includes a palladium alloy, a conductive carbon material that supports the palladium alloy, and a proton conductive polymer electrolyte.

  The palladium alloy is a component that acts as a catalyst in the catalyst layer. Usually, a platinum-based catalyst is used. By using a palladium alloy for all or part of the catalyst, the raw material cost of the catalyst can be reduced. Further, by using a palladium alloy as a catalyst in the catalyst layer, it is possible to exhibit excellent power generation characteristics and durability. In the catalyst layer, a catalyst component other than the palladium alloy may be used in combination, but preferably, the palladium alloy is contained in an amount of 10 to 100% by mass with respect to the total mass of the catalyst in the anode catalyst layer.

The palladium alloy is an alloy containing palladium as a main component. Since it is an alloy, a certain amount of impurities cannot be avoided, but it is preferably substantially free of platinum and composed of palladium and a metal other than platinum. As used herein, “substantially no platinum” includes an embodiment in which platinum is contained as an impurity. The platinum content is preferably 1% by mass or less, more preferably 0.5% by mass or less. Although it does not specifically limit as a specific example of a palladium alloy, A palladium-cobalt alloy is mentioned. By alloying palladium and cobalt, the crystal structure and the electronic state of the particle surface change, and the acid resistance can be improved.
The abundance ratio of palladium to cobalt in the palladium-cobalt alloy is preferably Pd / Co = 5/1 to 2/1 from the viewpoint of catalytic activity (hydrogen oxidation activity) in the anode catalyst layer.

  Moreover, it is preferable that the surface of the palladium-cobalt alloy is coated with palladium. That is, it is preferable to have a core-shell structure including a core made of a palladium-cobalt alloy and a shell made of palladium. By coating the surface of the palladium-cobalt alloy with palladium, elution of cobalt can be suppressed.

  The average particle diameter of the palladium alloy contained in the anode catalyst layer is not particularly limited, but is preferably 3 to 10 nm. When the particle diameter is in this range, the area where the electrochemical reaction proceeds is large, and the catalyst utilization rate can be increased. In addition, the average particle diameter of a palladium alloy is measured by measuring the particle diameter of the particle | grains observed in several to several tens visual fields about a sample, for example using a scanning electron microscope, and calculating an average value.

The conductive carbon material that supports the palladium alloy is a carbon material having a function as a catalyst carrier and having conductivity. Transfer of electrons at the site where the electrode reaction actually proceeds is performed through a conductive carbon material. The conductive carbon material for the anode catalyst layer is not particularly limited, but preferably includes carbon black and graphitized carbon black. Moreover, the palladium alloy carrying | support density | concentration of an electroconductive carbon material is although it does not specifically limit, It is preferable that it is 30-70 mass% with respect to the total mass of the electroconductive carbon material which is a support | carrier. The surface area of the conductive carbon material supporting the palladium alloy is preferably 300 to 1200 m ² / g.
Various methods such as an impregnation method, a coprecipitation method, a colloid method, a reverse micelle method, and a spray method can be used as a method for supporting a palladium alloy on a conductive carbon material. Among these, a colloid method and / or a reverse micelle method that can make the particle composition uniform and control the particle size are preferable.

  The proton conductive polymer electrolyte plays a role of increasing the mobility of protons moving between the cathode and the anode in PEFC power generation. The polymer electrolyte is not particularly limited as long as it is generally used in the catalyst layer. Specifically, a perfluorocarbon polymer having a sulfonic acid group such as Nafion (registered trademark of DuPont), a hydrocarbon polymer compound doped with an inorganic acid such as phosphoric acid, a part of which is proton-conductive Examples include organic / inorganic hybrid polymers substituted with functional groups, and polymer electrolytes such as proton conductors in which a polymer matrix is impregnated with a phosphoric acid solution or a sulfuric acid solution.

  The solid polymer electrolyte membrane 100 is an ion conductive membrane that exists between the cathode catalyst layer and the anode catalyst layer. The solid polymer electrolyte membrane is not particularly limited, and a membrane made of the same proton conductive electrolyte as that used for the catalyst layer can be used. For example, commercially available solid polymer electrolyte membranes such as various types of Nafion (registered trademark) manufactured by DuPont and perfluorosulfonic acid membranes represented by Flemion (registered trademark) can be used. A membrane in which a polymer microporous membrane is impregnated with a liquid electrolyte, a membrane in which a porous body is filled with a polymer electrolyte, or the like may be used. The polymer electrolyte used for the solid polymer electrolyte membrane and the proton conductive electrolyte used for the catalyst layer may be the same or different, but the adhesion between the catalyst layer and the solid polymer electrolyte membrane is From the viewpoint of improvement, it is preferable to use the same one.

  The thickness of the solid polymer electrolyte membrane may be appropriately determined in consideration of the properties of the obtained MEA, but is preferably not too thin from the viewpoint of strength during film formation and durability during use. From the viewpoint of the output characteristics, it is preferable that the thickness is not too thick. Specifically, the thickness of the solid polymer electrolyte membrane is preferably 5 to 300 μm, more preferably 10 to 200 μm, and particularly preferably 15 to 150 μm.

  The cathode catalyst layer 110 includes a catalyst, a conductive carbon material that supports the catalyst, and a proton conductive polymer electrolyte.

  In the cathode side catalyst layer, it is difficult to make the total amount of the catalyst a palladium alloy from the viewpoint of oxygen reduction activity and durability. For this reason, platinum or a platinum alloy is used as a catalyst like the conventional PEFC. Alternatively, platinum or a platinum alloy and a palladium alloy are used as the catalyst. Although it does not specifically limit as a platinum alloy, The alloy of platinum and iridium and the alloy of platinum and rhodium are mentioned. Since the palladium alloy is as described above in the description of the anode catalyst layer, the description is omitted here.

  In the embodiment in which the platinum-based catalyst and the palladium-based catalyst are used in combination, it is appropriate to properly use the platinum-based catalyst and the palladium-based catalyst depending on the site. It is possible to improve the durability of PEFC by using a platinum-based catalyst at a site where the catalyst is likely to deteriorate.

  For example, as shown in FIG. 2, the cathode catalyst layer has a two-layer structure of a first catalyst layer 112 and a second catalyst layer 114. Platinum or a platinum alloy is disposed on the first catalyst layer 112 on the solid polymer electrolyte membrane 100 side where the reaction tends to concentrate. A palladium alloy is disposed on the second catalyst layer 114 on the gas diffusion layer 120 side. Thus, platinum or platinum alloy is unevenly distributed on the solid polymer electrolyte membrane side, and palladium alloy is unevenly distributed on the side opposite to the solid polymer electrolyte membrane, thereby reducing the amount of platinum used and reducing the production cost of MEA. Can be reduced. Although FIG. 2 shows an embodiment in which the cathode catalyst layer has a two-layer structure, the layers may not be clearly separated. For example, an embodiment in which the blending ratio of the platinum-based catalyst and the palladium-based catalyst is gradually changed, an embodiment having a laminated structure of three or more layers, and the like can be given.

  As another mode in which the platinum-based catalyst and the palladium-based catalyst are selectively used, there is a mode in which the catalyst to be used is properly used according to the form of the flow path of the gas supplied to the cathode catalyst layer. Usually, the portion corresponding to the downstream side of the gas flow path 135 formed in the separator tends to be more deteriorated in the catalyst than the portion corresponding to the upstream side of the gas flow path 135. For this reason, a platinum-based catalyst is used for a portion corresponding to the downstream side of the gas flow path 135, and a palladium-based catalyst is used for a portion corresponding to the upstream side of the gas flow path 135. That is, platinum or platinum alloy is unevenly distributed downstream of the gas flow path through which the gas supplied to the cathode catalyst layer passes, and palladium alloy is placed upstream of the gas flow path through which the gas supplied to the cathode catalyst layer passes. Make it unevenly distributed.

The conductive carbon material in the cathode catalyst layer is a carbon material having a function as a catalyst carrier and having conductivity. Transfer of electrons at the site where the electrode reaction actually proceeds is performed through a conductive carbon material. Examples of the conductive carbon material for the cathode catalyst layer include carbon black and graphitized carbon black. By graphitizing carbon black, the number of functional groups to be hydrophilized such as hydroxyl groups and carboxyl groups present on the surface of carbon black can be reduced, and carbon black can be hydrophobized. In addition, when graphitized carbon black is used, it is possible to form a water-repellent gradient in the direction of the solid polymer electrolyte membrane-buffer layer-catalyst layer-gas diffusion layer, and promote the movement of water. is there. Moreover, it is preferable to increase the carbon corrosion resistance of the carbon material used for the cathode catalyst layer by using carbon black having a specific surface area of 80 to 350 m ² / g. Although the catalyst carrying | support density | concentration of an electroconductive carbon material is not specifically limited, From a viewpoint of preventing the corrosion of a support | carrier, it is preferable that it is 30-70 mass% with respect to the total mass of the electroconductive carbon material which is a support | carrier.

  Preferably, carbon black that has been further hydrophobized with a fluorine compound is used as the conductive carbon material of the cathode catalyst layer. This improves the hydrophobicity of the cathode catalyst layer. The amount of carbon black hydrophobized using a fluorine compound is preferably 1 to 20% by mass with respect to the total mass of the conductive carbon material of the cathode catalyst layer. By blending an amount in this range, high power generation performance can be developed from the initial stage to after a long period of time and from low current density to high current density, durability can be improved, and high life characteristics can be realized.

  An example of the hydrophobization treatment is a method of treating carbon black with polytetrafluoroethylene.

  Preferably, carbon nanotubes, carbon nanofibers, or carbon nanohorns are further used as the conductive carbon material of the cathode catalyst layer. By adding carbon nanotubes, carbon nanofibers, or carbon nanohorns that have a higher degree of graphitization than carbon black, the hydrophobicity in the cathode catalyst layer is improved and the destruction of the three-phase structure due to deterioration is suppressed. Can do. Depending on the case, two or three types of carbon nanotubes, carbon nanofibers, or carbon nanohorns may be used in combination. The usage-amount of a carbon nanotube, carbon nanofiber, or carbon nanohorn is 1-20 mass% with respect to the total mass of the electroconductive carbon material of a cathode catalyst layer. By blending an amount in this range, high power generation performance can be exhibited from the initial stage to after a long period of time and from low current density to high current density, durability can be improved, and high life characteristics can be realized.

  Carbon nanotubes, carbon nanofibers, and carbon nanohorns may be included in the cathode catalyst layer without supporting the catalyst.

  The proton conductive polymer electrolyte is the same as described in the description of the anode catalyst layer, and therefore the description thereof is omitted here.

  The MEA of the present invention is excellent in power generation characteristics and can be manufactured at low cost. And PEFC produced using MEA of this invention can be manufactured at low cost. In addition, the durability is excellent, and even when PEFC is used for a long period of time, the power generation characteristics are hardly deteriorated. Such characteristics are particularly beneficial in applications that require durability over a long period of time. Such applications include vehicles. Since the power generation characteristics of the PEFC of the present invention can be maintained over a long period of time, the life of a vehicle equipped with the PEFC of the present invention can be prolonged and the vehicle value can be improved.

  Hereinafter, the present invention will be described more specifically with reference to examples. In addition, this invention is not limited to the following Example.

Example 1
1. Preparation of anode catalyst As a conductive material, 4 g of carbon black (Ketjen Black ^TM EC, manufactured by Ketjen Black International Co., Ltd., BET surface area = 800 m ² / g) was prepared.

  Ketjen Black EC 4.0 g and cobalt nitrate aqueous solution (Co concentration 0.5%) 100 g were added and stirred for 1 hour. Further, 50 g of an aqueous tetramethylammonium hydroxide solution (concentration: 0.5%) was mixed as a reducing agent and stirred for 1 hour.

  Next, 400 g of an aqueous palladium nitrate solution (Pd concentration: 1.0%) was added to the mixed solution and stirred for 1 hour, and 50 g of propanol as a reducing agent was further mixed and stirred for 1 hour. Then, it heated up to 60 degreeC in 30 minutes, and stirred at 60 degreeC for 12 hours. Then, it heated up to 90 degreeC in 30 minutes, and also, after stirring at 90 degreeC for 12 hours, it cooled to room temperature in 1 hour. After filtering the precipitate, the obtained solid was dried under reduced pressure at 85 ° C. for 12 hours and pulverized in a mortar. This was heat-treated at 650 ° C. for 2 hours under an inert gas atmosphere to prepare palladium-cobalt (Pd / Co = 3/1) -supported carbon, which was used as an anode catalyst.

2. Preparation of Cathode Catalyst Graphitized carbon black (graphitized Ketjen black) is obtained by graphitizing carbon black (Ketjen Black ^TM EC manufactured by Ketjen Black International) at 2700 ° C. for 10 hours. It was. 400 g of a dinitrodiammine platinum aqueous solution (Pt concentration: 1.0%) was added to 4.0 g of Ketjen Black subjected to graphitization treatment, followed by stirring for 1 hour. Further, 50 g of formic acid as a reducing agent was mixed and stirred for 1 hour. Then, it heated up to 40 degreeC in 30 minutes, and stirred at 40 degreeC for 6 hours. The mixture was heated to 60 ° C. in 30 minutes, further stirred at 60 ° C. for 6 hours, and then cooled to room temperature in 1 hour. After filtering the precipitate, the obtained solid was dried under reduced pressure at 85 ° C. for 12 hours and pulverized in a mortar to prepare platinum-supported carbon, which was used as a cathode catalyst.

3. Preparation of anode catalyst layer 5 times the amount of purified water was added to the mass of the anode catalyst, and vacuum degassing operation was added for 5 minutes. To this, 0.5 times the amount of n-propyl alcohol was added, and a solution containing a proton conductive polymer electrolyte (containing 20 wt% Nafion (registered trademark) manufactured by DuPont) was added. The obtained mixed slurry was well dispersed with an ultrasonic homogenizer, and a catalyst slurry was prepared by applying a vacuum degassing operation. An amount of the catalyst slurry corresponding to the desired thickness was printed on one side of the polytetrafluoroethylene sheet by screen printing and dried at 60 ° C. for 24 hours. The size of the formed anode catalyst layer was 5 cm × 5 cm. The coating layer on the polytetrafluoroethylene sheet was adjusted so that the amount of catalyst metal was 0.4 mg / cm ² .

4). Preparation of cathode catalyst layer 5 times the amount of purified water was added to the mass of the cathode catalyst, and vacuum degassing operation was added for 5 minutes. To this, 0.5 times the amount of n-propyl alcohol was added, and a solution containing a proton conductive polymer electrolyte (containing 20 wt% Nafion (registered trademark) manufactured by DuPont) was added. The obtained mixed slurry was well dispersed with an ultrasonic homogenizer, and a catalyst slurry was prepared by applying a vacuum degassing operation. An amount of the catalyst slurry corresponding to the desired thickness was printed on one side of the polytetrafluoroethylene sheet by screen printing and dried at 60 ° C. for 24 hours. The size of the formed cathode catalyst layer was 5 cm × 5 cm. The coating layer on the polytetrafluoroethylene sheet was adjusted so that the amount of catalyst metal was 0.4 mg / cm ² .

5. Joining to a solid polymer electrolyte membrane As a solid polymer electrolyte membrane, Nafion ^™ 111 (film thickness 25 µm) and a catalyst layer formed on the previously prepared polytetrafluoroethylene sheet were superposed. At that time, the anode catalyst layer, the solid polymer electrolyte membrane, and the cathode catalyst layer were laminated in this order. Thereafter, hot pressing was performed at 130 ° C. and 2.0 MPa for 10 minutes.

6). MEA Performance Evaluation After joining the catalyst layer and the solid polymer electrolyte membrane, a gas diffusion layer (GDL) was placed outside thereof to produce a membrane electrode assembly (MEA). A gas separator with a gas flow path was disposed on both surfaces of the MEA, and was further sandwiched between gold-plated stainless steel current collector plates to form a single cell for evaluation. In the evaluation unit cell, hydrogen was supplied as a fuel to the anode side, and air was supplied as an oxidant to the cathode side. The supply pressure of both gases was atmospheric pressure, hydrogen was set to 58.6 ° C. and relative humidity 60%, air was set to 54.8 ° C. and relative humidity 50%, and the cell temperature was set to 70 ° C. The hydrogen utilization rate was 67% and the air utilization rate was 40%. Under this condition, the cell voltage when power was generated at a current density of 1.0 A / cm ² was measured as the initial cell voltage.

Subsequently, power generation was stopped after generating power for 60 seconds. After stopping, the supply of hydrogen and air was stopped, the single cell was replaced with air, and the system was on standby for 50 seconds. Thereafter, hydrogen gas was supplied to the anode side for 10 seconds at 1/5 of the above utilization rate. Thereafter, hydrogen gas was supplied to the anode side and air was supplied to the cathode side under the same conditions as described above, and power was generated again at a current density of 1.0 A / cm ² for 60 seconds. The load current at this time was increased from 0 A / cm ² to 1 A / cm ² in 30 seconds. This power generation / stop operation was performed, the cell voltage was measured, and the power generation performance was evaluated. The number of cycles when the cell voltage at a current density of 1.0 A / cm ² was 0.45 V was used as the durability evaluation value. The configuration and results are shown in Table 1.

(Example 2)
A PEFC was produced in the same manner as in Example 1 except that the amount of the catalyst metal of the anode catalyst was adjusted to 0.1 mg / cm ² . The power generation performance was evaluated for this evaluation PEFC. The configuration and results are shown in Table 1.

(Example 3)
A PEFC was produced in the same manner as in Example 2 except that a platinum-cobalt alloy was used as the cathode catalyst. The power generation performance was evaluated for this evaluation PEFC. The configuration and results are shown in Table 1.

Example 4
400 g of a palladium-cobalt (Pd / Co = 3/1) trimethylammonium complex-protected colloid (TMA colloid) dispersion (Pd concentration 1%) was added to carbon black (Ketjen Black ^™ EC, BET manufactured by Ketjen Black International). 4 g of surface area = 800 m ² / g) was added and stirred for 1 hour. Furthermore, it stirred for 1 hour, bubbling carbon monoxide gas as a reducing agent. Thereafter, the mixture was heated to 60 ° C. in 30 minutes, stirred at 60 ° C. for 12 hours, and then cooled to room temperature in 1 hour. After filtering the precipitate, the obtained solid was dried under reduced pressure at 85 ° C. for 12 hours and pulverized in a mortar. This was heat-treated at 650 ° C. for 2 hours under an inert gas atmosphere to obtain an anode catalyst in which palladium-cobalt (Pd / Co = 3/1) was supported on the carbon black.

A PEFC was produced in the same manner as in Example 1 except that the anode catalyst was used and the amount of catalyst metal in the anode catalyst layer was adjusted to 0.1 mg / cm ² . The power generation performance was evaluated for this evaluation PEFC. The configuration and results are shown in Table 1.

(Example 5)
The cathode catalyst layer is made into a two-layer structure according to the following procedure, except that the first cathode catalyst layer is in contact with the solid polymer electrolyte membrane and the second cathode catalyst layer is in contact with the gas diffusion layer when the MEA is produced. Produced a PEFC in the same manner as in Example 2.

Five times the amount of purified water was added to the mass of the Pd—Co-supported carbon, and a vacuum degassing operation was added for 5 minutes. To this, 0.5 times the amount of n-propyl alcohol was added, and a solution containing a proton conductive polymer electrolyte (containing 20 wt% Nafion (registered trademark) manufactured by DuPont) was added. The obtained mixed slurry was well dispersed with an ultrasonic homogenizer, and a catalyst slurry was prepared by applying a vacuum degassing operation. The catalyst slurry in an amount corresponding to a desired thickness is printed on one side of the polytetrafluoroethylene sheet by a screen printing method and dried at 60 ° C. for 24 hours. A coated sheet A on which a cathode catalyst layer was formed was obtained. The size of the formed second cathode catalyst layer was 5 cm × 5 cm. The coating layer on the polytetrafluoroethylene sheet was adjusted so that the amount of catalyst metal was 0.2 mg / cm ² .

Next, 5 times the amount of purified water was added to the mass of the Pt-supported carbon, and a vacuum degassing operation was added for 5 minutes. To this, 0.5 times the amount of n-propyl alcohol was added, and a solution containing a proton conductive polymer electrolyte (containing 20 wt% Nafion (registered trademark) manufactured by DuPont) was added. The obtained mixed slurry was well dispersed with an ultrasonic homogenizer, and a catalyst slurry was prepared by applying a vacuum degassing operation. The first cathode catalyst is obtained by printing a catalyst slurry in an amount corresponding to a desired thickness on the coated sheet A by screen printing on one side of a polytetrafluoroethylene sheet and drying at 60 ° C. for 24 hours. A layer was made. The size of the first cathode catalyst layer to be formed was 5 cm × 5 cm. In addition, the entire coating layer on the polytetrafluoroethylene sheet was adjusted so that the amount of catalyst metal was 0.4 mg / cm ² (Pt 0.2 mg / cm ² , Pd—Co 0.2 mg / cm ² ).

Incidentally, Pt-loaded carbon was used for the first cathode catalyst layer, platinum as a catalyst, by carbon black carrier (Ketjen Black International Co. Ketjenblack ^{TM EC)} for processing 10 hours graphitized at 2700 ° C., Graphitized carbon black (graphitized ketjen black) was used. The Pd—Co-supported carbon used for the second cathode catalyst layer is graphitized at 2700 ° C. for 10 hours using a palladium-cobalt alloy as a catalyst and carbon black (Ketjen Black ^™ EC manufactured by Ketjen Black International Co., Ltd.) as a carrier. By processing, carbon black (graphitized Ketjen black) that was graphitized was used.

(Example 6)
A PEFC was produced in the same manner as in Example 5 except that carbon nanofibers were blended in the cathode catalyst layer. The power generation performance was evaluated for this evaluation PEFC. The configuration and results are shown in Table 1.

(Comparative Example 1)
As an anode catalyst, except for using carbon black carrying a platinum (Ketjen Black International Co. Ketjenblack ^{TM EC)} was prepared PEFC in the same manner as in Example 1. The power generation performance was evaluated for this evaluation PEFC. The configuration and results are shown in Table 1.

(Comparative Example 2)
As an anode catalyst, except for using carbon black carrying a platinum (Ketjen Black International Co. Ketjenblack ^{TM EC)} was prepared PEFC in the same manner as in Example 2. The power generation performance was evaluated for this evaluation PEFC. The configuration and results are shown in Table 1.

(Comparative Example 3)
As the cathode catalyst, a palladium - cobalt alloy except for using carbon black carrying (Ketjen Black International Co. Ketjenblack ^{TM EC)} and was prepared PEFC in the same manner as in Comparative Example 1. The power generation performance was evaluated for this evaluation PEFC. The configuration and results are shown in Table 1.

  From Table 1, it can be seen that a PEFC having excellent power generation characteristics and excellent durability can be produced using a palladium alloy as a catalyst in the anode catalyst layer. In addition, the comparison between Examples 5 and 6 shows that the durability of PEFC is improved by adding carbon nanofibers.

  Subsequently, the effects of catalyst alloying and support graphitization were investigated by the following method.

  A single cell for evaluation was produced in the same manner as in Example 1 except that the catalyst and carrier shown in Table 2 were used. Hydrogen was supplied as a fuel to the anode side of the evaluation single cell, and nitrogen was supplied to the cathode side. The supply pressure for both gases is atmospheric pressure, hydrogen is set at a flow rate of 100 L / min at a relative humidity of 100%, nitrogen is set at a flow rate of 200 L / min at a relative humidity of 100%, the cell temperature is set at 70 ° C., and the potential is set at 0.04 V to 0 The current was taken out by operating up to .9 V, and a CV curve was obtained. From the hydrogen adsorption peak of this CV curve, the initial electrochemical surface area (ECA) was determined.

  Next, hydrogen was supplied as fuel to the anode side of the evaluation unit cell, and nitrogen was supplied to the cathode side. The supply pressure for both gases is atmospheric pressure, hydrogen is set at a flow rate of 500 L / min at a relative humidity of 100%, nitrogen is set at a flow rate of 500 L / min at a relative humidity of 100%, the cell temperature is set at 70 ° C. A potential of .95 V was repeatedly applied at a cycle of 5 seconds. After the potential application operation was performed 7520 times, hydrogen was supplied as fuel to the anode side, and nitrogen was supplied to the cathode side. The supply pressure for both gases is atmospheric pressure, hydrogen is set at a flow rate of 100 L / min at a relative humidity of 100%, nitrogen is set at a flow rate of 200 L / min at a relative humidity of 100%, the cell temperature is set at 70 ° C., and the potential is set at 0.04 V to 0 The current was taken out by operating up to .9 V, and a CV curve was obtained. The electrochemical surface area (ECA) after the potential cycle test was determined from the hydrogen adsorption peak of this CV curve.

  The ECA decrease rate at the cathode was calculated from the initial ECA and the ECA after the potential cycle test. The ECA reduction rate was determined by ECA reduction rate (%) = 100− (ECA after potential cycle test / initial ECA) × 100. It shows that it is excellent in durability, so that ECA fall rate is small.

  As shown in Table 2, it can be seen that by alloying platinum or palladium, the durability is improved and the ECA reduction rate is reduced. It can also be seen that graphitizing the carrier improves durability and reduces the ECA reduction rate.

  The PEFC of the present invention is used as various power sources. The PEFC of the present invention that is excellent in durability is used as a power source of a vehicle, for example.

It is a cross-sectional schematic diagram of one Embodiment of PEFC of this invention. It is a cross-sectional schematic diagram of PEFC in which the cathode-side catalyst layer has a two-layer structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... PEFC, 20 ... MEA, 100 ... Solid polymer electrolyte membrane, 110 ... Catalyst layer, 112 ... 1st catalyst layer, 114 ... 2nd catalyst layer, 120 ... Gas diffusion layer, 130 ... Separator, 135 ... Channel, 140 ... Current collector.

Claims (15)

An anode catalyst layer comprising a palladium alloy, a conductive carbon material supporting the palladium alloy, and a proton-conductive polymer electrolyte;
A solid polymer electrolyte membrane;
A cathode catalyst layer comprising a catalyst, a conductive carbon material supporting the catalyst, and a proton-conductive polymer electrolyte;
A membrane electrode assembly. 2. The membrane / electrode assembly according to claim 1, wherein the content of the palladium alloy is 10 to 100 mass% with respect to the total mass of the catalyst in the anode catalyst layer. The membrane electrode assembly according to claim 1 or 2, wherein the palladium alloy is a palladium-cobalt alloy. The membrane electrode assembly according to claim 3, wherein the abundance ratio of palladium to cobalt in the palladium-cobalt alloy is Pd / Co = 5/1 to 2/1. The membrane electrode assembly according to claim 3 or 4, wherein the palladium-cobalt alloy has a surface coated with palladium metal. The membrane electrode assembly according to any one of claims 1 to 5, wherein an average particle diameter of the palladium alloy is 3 to 10 nm. The conductive carbon material carrying the palladium alloy is carbon black or graphitized carbon black, and the carrying concentration of the palladium alloy is 30 to 70% by mass with respect to the total mass of the carrier. 7. The membrane electrode assembly according to any one of 6 above. The membrane electrode assembly according to any one of claims 1 to 7, wherein the palladium alloy is supported on the conductive carbon material by a colloidal method and / or a reverse micelle method. The membrane electrode assembly according to any one of claims 1 to 8, wherein a catalyst of the cathode catalyst layer is platinum, a platinum alloy, or a palladium alloy. The membrane electrode assembly according to claim 9, wherein the platinum or the platinum alloy is unevenly distributed on the solid polymer electrolyte membrane side, and the palladium alloy is unevenly distributed on the side facing the solid polymer electrolyte membrane. The platinum or the platinum alloy is unevenly distributed downstream of the gas flow path through which the gas supplied to the cathode catalyst layer passes, and the palladium alloy is a gas flow path through which the gas supplied to the cathode catalyst layer passes. The membrane electrode assembly according to claim 9, wherein the membrane electrode assembly is unevenly distributed upstream. The carbon black hydrophobized using a fluorine compound as the conductive carbon material of the cathode catalyst layer is contained in an amount of 1 to 20% by mass based on the total mass of the conductive carbon material of the cathode catalyst layer. The membrane electrode assembly according to any one of 1 to 11. The conductive carbon material of the cathode catalyst layer includes carbon nanotubes, carbon nanofibers, or carbon nanohorns in an amount of 1 to 20% by mass based on the total mass of the conductive carbon material of the cathode catalyst layer. 13. The membrane electrode assembly according to any one of 12 above. A polymer electrolyte fuel cell comprising the membrane electrode assembly according to any one of claims 1 to 13. A vehicle on which the polymer electrolyte fuel cell according to claim 14 is mounted.

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